Ali reported: I said to the Prophet, peace and blessings be upon him, “Your uncle, the misguided old man, has died.” The Prophet said, “Go bury your father and do nothing until you come back to me.” I buried him and I came back to him. The Prophet ordered me to bathe myself and he supplicated for me.

Source: Sunan Abī Dāwūd 3214

Grade: Sahih(authentic) according to Al-Albani

Al-Marghinani said, “If an unbeliever dies and his closest relative is a Muslim, then he washes him, shrouds him, and buries him.”